Various medical, industrial, and graphic imaging applications require the production of very high quality images on sheets or lengths of photothermographic materials. Sheets, lengths, and rolls of photothermographic materials are referred to as photothermographic elements. An exposed photothermographic element is thermally processed, that is, heated by a heated member within a processing apparatus, to at least a threshold development temperature for a specific period of time to develop the image within the photothermographic element. Subsequently, the photothermographic element must be cooled by a cooling member or apparatus within the processing apparatus to allow a user to hold the element while examining the developed image. Photothermographic elements generally include an emulsion coated onto a paper base or backing, or polyester film base. The emulsion coating, when heated, becomes soft and vulnerable to surface abrasions or marring, and delamination from the base during the transporting of the photothermographic element across components within the processing apparatus. One known cause of these problems is the component within the processing apparatus which directs the sheet away from the heated member, such as a heated, rotating drum, and toward the cooling apparatus.
Like the emulsion coating, the polyester film base softens when heated. In addition, the polyester film is susceptible to dimensional changes during heating and/or cooling. Uncontrolled dimensional changes which occur during cooling can results in wrinkling, especially when the rate of cooling the photothermographic material is increased. Increasing the cooling rate within known processing apparatus can increase productivity and/or reduce the space needed for cooling. But, increasing the cooling rate also can increase wrinkling.
One known apparatus and method for cooling includes a plurality of rotating nip rollers which withdraw the heat from each sheet after the sheet is processed by the heating component. Because the sheet shrinks as it cools, the constraining of the sheet by the nip rollers can cause wrinkles in the sheet which significantly affect the image quality. As shown in FIG. 1, opposing, diagonal wrinkles 2 in the polyester-film base 4 of the sheet 6 are caused by this constraint and appear like sloping branches of an evergreen tree.
Rollers present other problems. First, rollers can be difficult to keep clean. The emulsion 8 from the sheet 6, when heated, can gradually transfer from the sheet and build-up on the rollers which are not easily cleaned. A build-up of emulsion 8 on the cooling surface can change the conductivity and cooling effectiveness of the rollers, and the build-up can retransfer to subsequent sheets. Furthermore, known cooling rollers are not inexpensive and can include several parts to function smoothly, which adds complexity to the installation, cleaning, and repair of the rollers.
In addition to wrinkling and emulsion transfer, a heated and cooled sheet can suffer from excessive curling. This can occur because the sheet is heated when on a curved surface such as a rotating drum. As shown in FIG. 1, a curl C in a sheet 6 of radiographic film (used for medical diagnoses) causes the sheet 6 to lift away from the lightbox 9. At the very least, this inconveniences the medical specialist who is attempting to examine the sheet 6. Like radiographic film sheets, image-setting sheets and other sheets can suffer from undesirable curling.
There is a need for a cooling apparatus or article and method which offers sufficient cooling productivity, cost-effectiveness, and ease of assembly and repair, but without causing an unacceptable amount of wrinkling and curling within the sheet base and scratches in the sheet base or emulsion. In conjunction with this cooling apparatus or article, there is a need for a component which properly directs the sheet from the heating member to the cooling apparatus or article, but without delaminating or stripping the soft emulsion away from the base.